In the intermittent production of small hardened glass sheets, such as automobile side window panes, the process is as follows:
I. The suspension of several glass sheets by means of pinchers or clamps from a conveyor which moves along a rail; PA0 II. Simultaneously heating the glass sheets in a furnace; and PA0 III. Simultaneously hardening the glass sheets with the assistance of compressed air cooling. PA0 I. a pair of compressed air caissons, PA0 II. the elementary caissons being;
The compressed air cooling utilized in intermittent production is characterized by diametrically opposed caissons having large opposed surface areas equipped with openings for compressed air emissions.
In the prior art process, the progressive working station movement is accomplished by means of jolts or sudden starts. The conveyor from which the glass sheets are suspended moves from one working position to the following one at a preset rhythm.
The intermittent glass sheet hardening process is still advantageous in principle. The hardening of a plurality of relatively small glass sheets is limited by the caisson surface area capacity. Prior art production, however, has shown non-uniformity among suspended glass sheets being hardened. The non-uniformity exists even among sheets located on a common conveyor. The thinner the glass sheets, the more evident is the non-uniformity. For example, in a sheet whose thickness is only 3 mm., the hardening irregularities are such that it is no longer possible to guarantee the degree of fragmentation uniformity necessary in security window panes.
Uniform hardening difficulties normally arise when caissons are either perforated over their frontal surface or have relatively short compressed air cooling pipes. Caissons provided with relatively long pipes, greater than 20 cm., have a less serious air evacuation problem. The air flow exits between the long tubes forming the compressed air cooling pipes. Long pipe caissons, however, present numerous disadvantages that result in industrial utilization of short-pipe caissons whenever possible.
The present invention discloses an improved process and apparatus for simultaneous thermic glass sheet hardening whereby uniform hardening without sheet surface area defects is achieved. The improvement results without a considerable increase in production costs, even where the simultaneous hardening involves a plurality of thin sheets.